aEight-year-old Anita Ghai was buried in an earthen grave during a solar eclipse, while her mother was pressured to chant verses from Hindu scriptures – apparently to cure Ghai of polio, Which he had contracted at this age. of two. Ghai, now 67 years old and dean at Delhi’s Ambedkar University, says, “I still have the guilt that my mother had to endure because of me.”
Ghai thought such nightmares were over when, in March 2014, the World Health Organization declared India – home to half the world’s polio cases in 2009 – free of the disease. Yet, eight years later, a worrying sequence of events is underway around the world. Pakistan has seen a series of fresh cases, ending the 15-month period without a single new instance of polio. The wild virus from Pakistan has spread infection in Mozambique and Malawi, which were previously free of the disease.
In June, WHO reported cases of vaccine-derived polio – where a weakened virus in the vaccine spreads into the environment and infects people – in Eritrea, Ghana, Togo, Ivory Coast, Israel, Yemen, Nigeria and the Democratic Republic of . Congo. And in July, a patient in a New York City suburb was diagnosed with vaccine-derived polio. Over the past six weeks, traces of this form of the virus have also been found in sewage samples in Kolkata and London.
These seemingly unrelated cases highlight a common threat: Globally, polio vaccination levels in 2021 fell to the lowest in 15 years, according to WHO data, with immunization initiatives disrupted during Covid. India and Indonesia, the world’s two most populous countries, have seen a particularly sharp drop in vaccine coverage.
Experts say this makes recent cases a canary in a coal mine – warning that the paralyzing disease that ends up in much of the world could return, especially in densely populated areas, unless countries are vaccinated. And don’t redouble your efforts on surveillance.
“It was quite scary,” says virologist T Jacob John, of the traces of the virus found in the sewers of Kolkata, one of the founders of India’s polio vaccination programme. “A few more cases like this and we could see an outbreak.”
It’s not just a hypothetical scenario: 18 years after the country was declared free of the disease, Papua New Guinea suffered an outbreak of vaccine-derived polio infection in 2018.
Experts say there is no evidence so far that the recent cases represent an uncontrolled spread of the virus, at least in the US, UK and India. In Kolkata, investigators surveyed all neighborhoods where traces of the virus were found, to ensure that no one was potentially infected with polio.
Health officials were able to trace the cases – and traces in sewage – point to the strength of surveillance systems in these countries. “This is reassuring to me,” says Raman Bhatia, a veteran Indian polio vaccine campaigner associated with Rotary International, which is one of the pillars of the global polio vaccination effort.
But like vaccination levels, routine screening for cases of polio-associated paralysis has also declined over the past two years. In Indonesia, researchers found that such surveillance was severely disrupted during the pandemic.
This is bad news, says Luthfi Azizatunnisa, a public health researcher at Yogyakarta-based Universitas Gadja Mada and lead author of the Indonesian study. She says the country has areas with low vaccination coverage. “When surveillance is disrupted, we may never know or remember poliovirus spreading in the environment or community.”
Overall, the global polio burden from the wild virus has decreased by 99% since 1988, when the disease was endemic in more than 125 countries and infected 350,000 people a year. Today, those countries are reduced to just two: Pakistan and Afghanistan.
The rise in cases of vaccine-derived polio has reopened debate among some experts over the benefits of the two main types of vaccinations commonly used against the disease.
The first, known as IPV, uses an inactivated virus and is injected. The second, administered orally, is known as OPV and is a weakened but active virus that, once circulating in a population, can mutate and sometimes cause outbreaks.
“Countries that use specific IPVs are not at risk of generating new circulating vaccine-derived polioviruses,” says Walter Orenstein, former director of the US National Immunization Program. For this reason, Western countries are almost entirely dependent on IPV. But they may also accidentally import vaccine-derived polio from countries where OPV is used, he says.
Drops are easier to administer than injections because they don’t require qualified medical professionals, says Jay Wenger, director of the polio team at the Bill & Melinda Gates Foundation. According to Steven Wasilak, associate chief of science in the Global Immunization Division of the US Centers for Disease Control and Prevention (CDC), OPV is more potent than IPV in preventing transmission of the polio virus, both orally and through feces. “OPV makes sense in developing countries where sanitation is a challenge,” he says.
John isn’t convinced: In a paper published in July in the Lancet medical journal, he questioned the evidence behind the notion that the virus is primarily transmitted by oral or fecal routes in poor countries.
What is clear is that like the wild virus, vaccine-derived polio tends to find victims among unvaccinated people. People who have received all of their doses are immune to most vaccine-derived viruses if they are exposed to it in air or water.
“The primary risk factor for any poliovirus – whether wild or vaccine-derived – is low vaccination coverage,” says Zubair Vadud, a Geneva-based epidemiologist at the WHO. “If a population is fully vaccinated, they will be protected against any type of poliovirus.”
If vaccination levels drop below 80%, the risk increases, says John Ross, MD, assistant professor of medicine at Harvard Medical School. This “creates an opening for the vaccine-derived poliovirus to circulate, increasing the risk of it returning to a virulent form”, he says.
Aziztunnisa suggests that Indonesia may be particularly vulnerable, using a combination of OPV and IPV vaccines. According to WHO and UNICEF, the country’s polio vaccination rate dropped to 68% in 2021. India also largely depends on OPV, although the vaccination rate has not fallen below 80%.
Disinformation and conspiracy theories reached new heights amid the pandemic, says Vasilak, which also affected rates. “Today, this is a challenge we must face in order to bring vaccination levels up again.”
Wealthy countries should not leave their poor neighbors alone to deal with declining vaccination numbers, but donor countries and agencies should increase their support for the Global Polio Eradication Initiative, a public-private coalition including the Gates Foundation, CDC, WHO and the Global Polio Eradication Initiative. , UNICEF, Rotary International and Gavi, the vaccine alliance, says Wenger.
For health veterans like Orenstein, it’s a wake-up call. “We are still at risk,” he says. For patients like Ghai, the consequences of sliding against a debilitating disease are more personal.
“My parents taught me never to give up,” says the Delhi professor. “I did not let polio defeat me. Neither should the world.”
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